It's a pretty basic question, so here's my answer.
To stay focused I actually pushed my start menu (i'm on a windows machine) to the right side of the screen. This way I am not constantly reminded of other pages and I am more inclined to actually do something.
Ontop of that I also only have 1 instant messaging service (Skype) that I use currently. And the only people on that account are important business partners or very important friends. To talk with actual friends, I actually prefer to use email versus social networks like Facebook or Twitter, this way I'm not constantly checking them.
Anyways, those are my main methods, what are yours?